The invention relates to an opto-electrical structural device or element made of silicon for detecting light in the wavelength band between 8 and 12 .mu.m with a Schottky transition or junction of p-doped silicon and a metal having a prescribed work function or electron affinity.
Detectors made of semiconducting silicon play a very important role in the photodetection of light in the visible and near infrared range of the spectrum. The Si-detectors are constructed, for instance, in the form of pn-photodiodes, PlN-photocells, Schottky barrier cells or elements, or MOS cells. These Si-structural elements have a high quantum yield or efficiency in the visible and near infrared range. A further advantage of using Si is seen in that, due to the highly developed technology of this material, one may now produce one-dimensional lines as well as so-called two-dimensional arrays, which comprise a plurality of consistently or uniformly sensitive detectors, for instance 256.times.256 with dimensions of 25.times.25 .mu.m (micrometer). Additionally, the signal-reading and further processing of the signals from the separate detector elements may be achieved by structural elements which are likewise integrated in the same silicon chip, which also comprises the detector elements. This method of construction is in a high state of development; solid state vidicons are already being produced based on silicon technologies.
The detection and imaging of light with wavelengths greater than 1 .mu.m, especially in the spectral bands 3-5 .mu.m and 8-12 .mu.m, is of great interest. Semiconductors having small energy gaps matched to this spectral band are especially used for such detection. Such semiconductors are, for example, indium antimonide (InSb) and cadmium-mercury telluride (CdHgTe). Even though the crystal growth of these materials and the production of structural elements therefrom is considerably more difficult than with silicon, arrays with a relatively small number of detector elements have already been realized.
Furthermore, a certain success has been achieved in connection with a different type of silicon detector element which differs from the one described above, in that it has an infrared sensitivity in the range of 3-5.mu.. These prior art detectors take advantage of the effect of the so-called internal photo emission by means of a Schottky barrier. If contacts made of metal having an appropriate work function are applied to the front surface of suitably prepared silicon, then barriers result at the metal-silicon interface. These barriers are suitable for detecting infrared radiation in the range of 3-5 .mu.m. The precious metals palladium and platinum have been proven to be especially suitable for this range of the IR-spectrum. With Pt and p-doped Si, barriers of 0.27 eV are obtained. Reference is made in this connection, for example, to an article: "Evaluation of a Schottky IR-CCD Staring Mosaic Focal Plane" by B. Capone et al in SPIE, 156 Modern Utilization of Infrared Technology IV (1978)", or to an article entitled "Platinum Silicide Schottky-Barrier IR-CCD Image Sensors" by M. Kimata et al in the Japanese Journal of Applied Physics, Vol. 21, Pg. 231, (1982)". These detector elements possess--compared to intrinsic semiconductor detectors--a small quantum yield or efficiency, however they may be produced with very great uniformity and are therefore well-suited to the production of larger arrays with many detector elements. Suitable structures, e.g., the well known CCD's (Charge Coupled Devices), may be integrated into the silicon for the signal-reading of the individual detector signals.
It is known from Schottky's works, see e.g., "Fundaments of Semiconductor Devices", by E. S. Yang, McGraw-Hill Book Company, 1978, pg. 133" that by applying an electrical field E to a metal/semiconductor contact a reduction of the existing barriers, corresponding to ##EQU1## takes place, wherein: q=elemental charge, .epsilon.=absolute dielectric constant, and .epsilon..sub.Si =relative dielectric constant of silicon. However, the required high field E is only achieved at the interface metal/semiconductor, if the semiconductor is very highly doped, e.g., higher than 10.sup.17 doping atoms per cm.sup.3. Such a high doping leads to such a high reverse current flowing on the metal/semiconductor that the arrangement is totally unsuitable for use as a detector.